Relation of head capsule width to instar development in larvae of the range caterpillar, Hemileuca oliviae Cockerell (Lepidoptera: Saturniidae) [pests of grasslands in New Mexico]

A classification scheme for determining larval instars of the range caterpillar, Hemileuca oliviae Cockerell (Lepidoptera: Saturniidae), based on spine characteristics, is described. The scheme is tested favorably by plotting head capsule widths against the predicted instar. Head capsule growth approximately followed Dyar's rule, but a second degree polynomial equation (ln Y = -0.424 + 0.477X -$0.022{\rm X}^{2}$) more accurately described growth. Finally, a key for determining instars is developed from spine characteristics and head capsule widths.